/**
 * 把错误的数据转正
 * @private
 * @example strip(0.09999999999999998)=0.1
 */
 function strip(num, precision = 15) {
    return +parseFloat(Number(num).toPrecision(precision));
  }

/**
 * Return digits length of a number
 * @private
 * @param {*number} num Input number
 */

function digitLength(num) {
    // Get digit length of e
    const eSplit = num.toString().split(/[eE]/);
    const len = (eSplit[0].split('.')[1] || '').length - +(eSplit[1] || 0);
    return len > 0 ? len : 0;
}

/**
 * 把小数转成整数,如果是小数则放大成整数
 * @private
 * @param {*number} num 输入数
 */

function float2Fixed(num) {
    if (num.toString().indexOf('e') === -1) {
        return Number(num.toString().replace('.', ''));
    }
    const dLen = digitLength(num);
    return dLen > 0 ? strip(Number(num) * Math.pow(10, dLen)) : Number(num);
}

/**
 * 把递归操作扁平迭代化
 * @param {number[]} arr 要操作的数字数组
 * @param {function} operation 迭代操作
 * @private
 */
 function iteratorOperation(arr, operation) {
    const [num1, num2, ...others] = arr;
    let res = operation(num1, num2);
  
    others.forEach((num) => {
      res = operation(res, num);
    });
  
    return res;
  }
/**
 * 高精度乘法
 * @export
 */
export function times(...nums) {
    if (nums.length > 2) {
        return iteratorOperation(nums, times);
    }
    const [num1, num2] = nums;
    const num1Changed = float2Fixed(num1);
    const num2Changed = float2Fixed(num2);
    const baseNum = digitLength(num1) + digitLength(num2);
    const leftValue = num1Changed * num2Changed;

    // checkBoundary(leftValue);
  
    return leftValue / Math.pow(10, baseNum);
}
/**
 * 高精度除法
 * @export
 */
 export function divide(...nums) {
    if (nums.length > 2) {
      return iteratorOperation(nums, divide);
    }
  
    const [num1, num2] = nums;
    const num1Changed = float2Fixed(num1);
    const num2Changed = float2Fixed(num2);
    // checkBoundary(num1Changed);
    // checkBoundary(num2Changed);
    // 重要，这里必须用strip进行修正
    return times(num1Changed / num2Changed, strip(Math.pow(10, digitLength(num2) - digitLength(num1))));
  }
/**
 * 高精度加法
 * @export
 */
 export function plus(...nums) {
    if (nums.length > 2) {
      return iteratorOperation(nums, plus);
    }
  
    const [num1, num2] = nums;
    // 取最大的小数位
    const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
    // 把小数都转为整数然后再计算
    return (times(num1, baseNum) + times(num2, baseNum)) / baseNum;
  }
  
/**
 * 高精度减法
 * @export
 */
 export function minus(...nums) {
    if (nums.length > 2) {
      return iteratorOperation(nums, minus);
    }
  
    const [num1, num2] = nums;
    const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
    return (times(num1, baseNum) - times(num2, baseNum)) / baseNum;
  }

  /**
 * 四舍五入
 * @export
 */
export function round(num, ratio) {
    const base = Math.pow(10, ratio);
    let result = divide(Math.round(Math.abs(times(num, base))), base);
    if (num < 0 && result !== 0) {
      result = times(result, -1);
    }
    // 位数不足则补0
    return result;
  }

  export default {
    times,
    plus,
    minus,
    divide,
    round,
  };